import {Pos} from "../line/pos.js"
import {
    cursorCoords,
    displayHeight,
    displayWidth,
    estimateCoords,
    paddingTop,
    paddingVert,
    scrollGap,
    textHeight
} from "../measurement/position_measurement.js"
import {gecko, phantom} from "../util/browser.js"
import {elt} from "../util/dom.js"
import {signalDOMEvent} from "../util/event.js"

import {startWorker} from "./highlight_worker.js"
import {alignHorizontally} from "./line_numbers.js"
import {updateDisplaySimple} from "./update_display.js"

// SCROLLING THINGS INTO VIEW

// If an editor sits on the top or bottom of the window, partially
// scrolled out of view, this ensures that the cursor is visible.
export function maybeScrollWindow(cm, rect) {
    if (signalDOMEvent(cm, "scrollCursorIntoView")) return

    let display = cm.display, box = display.sizer.getBoundingClientRect(), doScroll = null
    if (rect.top + box.top < 0) doScroll = true
    else if (rect.bottom + box.top > (window.innerHeight || document.documentElement.clientHeight)) doScroll = false
    if (doScroll != null && !phantom) {
        let scrollNode = elt("div", "\u200b", null, `position: absolute;
                         top: ${rect.top - display.viewOffset - paddingTop(cm.display)}px;
                         height: ${rect.bottom - rect.top + scrollGap(cm) + display.barHeight}px;
                         left: ${rect.left}px; width: ${Math.max(2, rect.right - rect.left)}px;`)
        cm.display.lineSpace.appendChild(scrollNode)
        scrollNode.scrollIntoView(doScroll)
        cm.display.lineSpace.removeChild(scrollNode)
    }
}

// Scroll a given position into view (immediately), verifying that
// it actually became visible (as line heights are accurately
// measured, the position of something may 'drift' during drawing).
export function scrollPosIntoView(cm, pos, end, margin) {
    if (margin == null) margin = 0
    let rect
    if (!cm.options.lineWrapping && pos == end) {
        // Set pos and end to the cursor positions around the character pos sticks to
        // If pos.sticky == "before", that is around pos.ch - 1, otherwise around pos.ch
        // If pos == Pos(_, 0, "before"), pos and end are unchanged
        pos = pos.ch ? Pos(pos.line, pos.sticky == "before" ? pos.ch - 1 : pos.ch, "after") : pos
        end = pos.sticky == "before" ? Pos(pos.line, pos.ch + 1, "before") : pos
    }
    for (let limit = 0; limit < 5; limit++) {
        let changed = false
        let coords = cursorCoords(cm, pos)
        let endCoords = !end || end == pos ? coords : cursorCoords(cm, end)
        rect = {
            left: Math.min(coords.left, endCoords.left),
            top: Math.min(coords.top, endCoords.top) - margin,
            right: Math.max(coords.left, endCoords.left),
            bottom: Math.max(coords.bottom, endCoords.bottom) + margin
        }
        let scrollPos = calculateScrollPos(cm, rect)
        let startTop = cm.doc.scrollTop, startLeft = cm.doc.scrollLeft
        if (scrollPos.scrollTop != null) {
            updateScrollTop(cm, scrollPos.scrollTop)
            if (Math.abs(cm.doc.scrollTop - startTop) > 1) changed = true
        }
        if (scrollPos.scrollLeft != null) {
            setScrollLeft(cm, scrollPos.scrollLeft)
            if (Math.abs(cm.doc.scrollLeft - startLeft) > 1) changed = true
        }
        if (!changed) break
    }
    return rect
}

// Scroll a given set of coordinates into view (immediately).
export function scrollIntoView(cm, rect) {
    let scrollPos = calculateScrollPos(cm, rect)
    if (scrollPos.scrollTop != null) updateScrollTop(cm, scrollPos.scrollTop)
    if (scrollPos.scrollLeft != null) setScrollLeft(cm, scrollPos.scrollLeft)
}

// Calculate a new scroll position needed to scroll the given
// rectangle into view. Returns an object with scrollTop and
// scrollLeft properties. When these are undefined, the
// vertical/horizontal position does not need to be adjusted.
function calculateScrollPos(cm, rect) {
    let display = cm.display, snapMargin = textHeight(cm.display)
    if (rect.top < 0) rect.top = 0
    let screentop = cm.curOp && cm.curOp.scrollTop != null ? cm.curOp.scrollTop : display.scroller.scrollTop
    let screen = displayHeight(cm), result = {}
    if (rect.bottom - rect.top > screen) rect.bottom = rect.top + screen
    let docBottom = cm.doc.height + paddingVert(display)
    let atTop = rect.top < snapMargin, atBottom = rect.bottom > docBottom - snapMargin
    if (rect.top < screentop) {
        result.scrollTop = atTop ? 0 : rect.top
    } else if (rect.bottom > screentop + screen) {
        let newTop = Math.min(rect.top, (atBottom ? docBottom : rect.bottom) - screen)
        if (newTop != screentop) result.scrollTop = newTop
    }

    let screenleft = cm.curOp && cm.curOp.scrollLeft != null ? cm.curOp.scrollLeft : display.scroller.scrollLeft
    let screenw = displayWidth(cm) - (cm.options.fixedGutter ? display.gutters.offsetWidth : 0)
    let tooWide = rect.right - rect.left > screenw
    if (tooWide) rect.right = rect.left + screenw
    if (rect.left < 10)
        result.scrollLeft = 0
    else if (rect.left < screenleft)
        result.scrollLeft = Math.max(0, rect.left - (tooWide ? 0 : 10))
    else if (rect.right > screenw + screenleft - 3)
        result.scrollLeft = rect.right + (tooWide ? 0 : 10) - screenw
    return result
}

// Store a relative adjustment to the scroll position in the current
// operation (to be applied when the operation finishes).
export function addToScrollTop(cm, top) {
    if (top == null) return
    resolveScrollToPos(cm)
    cm.curOp.scrollTop = (cm.curOp.scrollTop == null ? cm.doc.scrollTop : cm.curOp.scrollTop) + top
}

// Make sure that at the end of the operation the current cursor is
// shown.
export function ensureCursorVisible(cm) {
    resolveScrollToPos(cm)
    let cur = cm.getCursor()
    cm.curOp.scrollToPos = {from: cur, to: cur, margin: cm.options.cursorScrollMargin}
}

export function scrollToCoords(cm, x, y) {
    if (x != null || y != null) resolveScrollToPos(cm)
    if (x != null) cm.curOp.scrollLeft = x
    if (y != null) cm.curOp.scrollTop = y
}

export function scrollToRange(cm, range) {
    resolveScrollToPos(cm)
    cm.curOp.scrollToPos = range
}

// When an operation has its scrollToPos property set, and another
// scroll action is applied before the end of the operation, this
// 'simulates' scrolling that position into view in a cheap way, so
// that the effect of intermediate scroll commands is not ignored.
function resolveScrollToPos(cm) {
    let range = cm.curOp.scrollToPos
    if (range) {
        cm.curOp.scrollToPos = null
        let from = estimateCoords(cm, range.from), to = estimateCoords(cm, range.to)
        scrollToCoordsRange(cm, from, to, range.margin)
    }
}

export function scrollToCoordsRange(cm, from, to, margin) {
    let sPos = calculateScrollPos(cm, {
        left: Math.min(from.left, to.left),
        top: Math.min(from.top, to.top) - margin,
        right: Math.max(from.right, to.right),
        bottom: Math.max(from.bottom, to.bottom) + margin
    })
    scrollToCoords(cm, sPos.scrollLeft, sPos.scrollTop)
}

// Sync the scrollable area and scrollbars, ensure the viewport
// covers the visible area.
export function updateScrollTop(cm, val) {
    if (Math.abs(cm.doc.scrollTop - val) < 2) return
    if (!gecko) updateDisplaySimple(cm, {top: val})
    setScrollTop(cm, val, true)
    if (gecko) updateDisplaySimple(cm)
    startWorker(cm, 100)
}

export function setScrollTop(cm, val, forceScroll) {
    val = Math.max(0, Math.min(cm.display.scroller.scrollHeight - cm.display.scroller.clientHeight, val))
    if (cm.display.scroller.scrollTop == val && !forceScroll) return
    cm.doc.scrollTop = val
    cm.display.scrollbars.setScrollTop(val)
    if (cm.display.scroller.scrollTop != val) cm.display.scroller.scrollTop = val
}

// Sync scroller and scrollbar, ensure the gutter elements are
// aligned.
export function setScrollLeft(cm, val, isScroller, forceScroll) {
    val = Math.max(0, Math.min(val, cm.display.scroller.scrollWidth - cm.display.scroller.clientWidth))
    if ((isScroller ? val == cm.doc.scrollLeft : Math.abs(cm.doc.scrollLeft - val) < 2) && !forceScroll) return
    cm.doc.scrollLeft = val
    alignHorizontally(cm)
    if (cm.display.scroller.scrollLeft != val) cm.display.scroller.scrollLeft = val
    cm.display.scrollbars.setScrollLeft(val)
}
